OBJECTIVE: To investigate the prevalence of body image (BI) dissatisfaction in adolescents. The study enrolled 641 adolescents aged 11 to 17 from the town of Saudades, Santa Catarina, Brazil. The prevalence of BI dissatisfaction was 60.4% (males = 54.5%, females = 65.7%; p < 0.05). Boys were more likely to wish to increase the size of their body silhouette (26.4%) while girls wished to reduce theirs (52.4%). Adolescents from urban areas manifested greater prevalence of BI dissatisfaction and were more likely to want to reduce their body silhouette. The reasons given by these adolescents for why they were dissatisfied with their body images were similar for both sexes (p = 0.156). When analyzed by neighborhood the urban adolescents said that their dissatisfaction was esthetic, whereas the rural adolescents said it was based on self-esteem. An association was detected between perceived BI and the reasons for dissatisfaction. Conclusions: Esthetics, self-esteem and health were the most common reasons for BI dissatisfaction among these adolescents. More than half of them were dissatisfied with their body silhouettes. Therefore, there is a need for interventions by health services and professionals in this age range in order to avoid possible future problems with eating disorders (anorexia, bulimia and vigorexia).